LCP — loading
Largest Contentful Paint measures main-content loading. Good: 2.5 seconds or less at the 75th percentile.
Core Web Vitals
Google's real-world page-experience metrics for loading speed, interaction responsiveness, and visual stability.
In plain language
Core Web Vitals measure loading, responsiveness, and layout stability using real-user data when enough is available.
Lab tests help diagnose issues; field data reflects real visits. These metrics cannot guarantee rankings or overall quality.
The foundation
What matters in Core Web Vitals
INP — responsiveness
Interaction to Next Paint measures responsiveness. Good: 200 milliseconds or less at the 75th percentile.
CLS — stability
Cumulative Layout Shift measures unexpected movement. Good: 0.1 or less at the 75th percentile.
Applied by The Forge
How we put it into practice
We use these measures to reduce waiting and keep pages responsive and stable.
Deliver the important content early
Use server rendering, caching, optimised images, and deliberate loading priorities.
Keep interactions responsive
Limit JavaScript and long tasks so controls respond quickly.
Reserve visual space
Reserve media dimensions and manage font loading to reduce layout shifts.
Measure lab and field data
Use lab tests to diagnose issues and field data to understand real visits.
A useful boundary
Limits to keep in mind
- Core Web Vitals are not the same thing as a Lighthouse performance score.
- Passing the thresholds does not guarantee rankings, conversions, or a satisfying overall experience.
- A single local test cannot represent the range of real devices, networks, pages, and visitors.
A concrete example
A stable service landing page
A service page loads its main content early, reserves image space, and responds quickly. Field data checks the experience of real visitors.
Further reading
Primary sources
Check the sources behind these explanations.
Related concept
Analytics & conversions: Analytics and Conversions
Measuring website use, with respect for visitors' choices, to understand what helps people take useful next steps.